How to convert a 3.0L to a 3.0LX?

craze1cars

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Hi, I'm new here. Just bought a 1992 Rinker 181 with a 3.0L. Tag on the motor states it has a max rpm of 4200 to 4600 and "Digital Electronic Ignition System." Looks like a Chevy distributor and coil to me. If I've picked the right motor in my Clymer's manual I believe it's probably 115hp. They also show a 3.0LX that's rated at 135hp with max rpm of 4400 to 4800. Must be the same block, as rebuild procedures show all the same dimensions in the manual. Do they have different heads? Could I find a used head from a LX and bolt it on my L to gain 20hp? Is is just a different cam? Carburation?<br /><br />I'm a hot-rod guy who modifies old V-8's all the time, so I'm curious if I can do the same with this motor and gain some power. What needs to be changed?<br /><br />Thanks for any insight.
 

Bondo

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Re: How to convert a 3.0L to a 3.0LX?

Well,<br />Years ago the Same motor was called a 140hp.........<br />The difference between the 115hp,+ the 135hp is How Tight you Spin it.........<br /><br />It's more Mathematics, than Mechanics...........<br /><br />It seems that you just bought the Wrong Boat..........<br />Either, Enjoy What you Have,<br />Or, Trade it for 1 with a Bigger Motor........<br />There are NO Tricks to make a 3.0l any bigger or faster than it IS...........<br /><br />It takes 6hp to 10hp to gain 1mph in a boat.......<br />The 3.0l just Doesn't have that Potential Available in it........<br /><br /><br />BTW, Welcome to iboats forums...............
 

Don S

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Re: How to convert a 3.0L to a 3.0LX?

Who knows, with a 92 boat, a previous owner may have put in a different engine and used the old cover with the decal on it, or a different cover that has the wrong decal on it. Look and see if there is a small metal tag over the starter with a serial number on it.<br />The LX does have a different head on it from the L, but both used the EST distributor or the Digital ignition.<br />If you have a serial number, we may be able to figure out what exactly you have, but like bondo said, their really isn't much you can do for the marine 3.0.
 

trog100

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Re: How to convert a 3.0L to a 3.0LX?

i went into this in some depth not long ago.. in 89 GM stopped making the 2.5 block.. at the same time merc introduced the 3.0LX rated at 130 horse and the 3.0L mysteriously got downrated from 130 to 115 horse.. <br /><br />the main difference is the that after 89 untill 94 the 3.0L none LX got fitted with the 2.5 cylinderhead either as a genuine attempt at downgrading it to the same horsepower as the now discontinued bottom of the range 2.5 or simply to use up old stocks of 2.5 heads..<br /><br />after 94 the LX seems to have disappeared from the line up and the 3.0L got its proper 3 litre head back and got rated at 130 horse again the same as it was up until 89..<br /><br />make sense of it if u will but i think it was marketing and money saving stuff.. the hybrid 3 litre block with the 2.5 litre head was now the bottom of the range engine and saved GM making 2.5 block pieces..<br /><br />i also think the 115 horse rating of the hybrid 3.0L is marketing nonsense and isnt exactly true.. the intention was to simply pretend that they still had a 115 horse engine in their line up..<br /><br />sooo its only 3.0L engines between the end of 89 and about 94/95-ish that have this weird 115 horse rating and the 2.5 head..<br /><br />i recon the hybrid 3.0L beast with the 2.5 head would still wang out about 130 horses anyways so trying to make an LX out of it is a waste of time.. <br /><br />i thought my engine was a hybrid which is what prompted me to find all this cr-p out.. but its a late 88 with the proper 3 litre cylinderhead and rated at 130 horse so in a way i wasted my time. but its usefull information for those that wonder..<br /><br />its also about this time that merc introduced the pointless ignition system.. which i think only came on the 3.0LX.. but at 130 horse exactly the same as the pre 89 3.0L this didnt produce any power increase.. but merc probably wanted folks to think it did praps.. i would also imagine the LX version cost more than the L.. and folks had to have some reason to buy it..<br /><br />i think merc horse power ratings are more about having a nice neat sales line up than what the engine actually produces.. bear in mind way back in the 70s the 2.5 used to be called a 120 and the 3.0 a 140..<br /><br />engine ID stamped on block next to distributor.. first two letter on the left..<br /><br />RA pre 89 3.0L 130 horse..<br /><br />RM after 89 3.0L 2.5 head 115 horse..<br /><br />RJ after 89 3.0L 2.5 head 115 horse..<br /><br />RN after 89 3.0LX 3.0 head 130 horse..<br /><br />RK after 89 3.0LX 3.0 head 130 horse..<br /><br />one quick way to tell which head u really have on these 89 to 94 engines is that the LX 3 litre head takes 14mm long reach sparkplugs the L 2.5 litre head takes 14mm standard reach plugs..<br /><br />course to add to the confusion my pre 89 (RA) 3 litre head takes the same standard reach 14mm plugs as the (RM-RJ) 2.5 head.. up and down and round and round they went.. he he he<br /><br />trog100
 

craze1cars

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Re: How to convert a 3.0L to a 3.0LX?

Thanks, especially Trog, for your extremely detailed info. I did a little more searching. Incidentally I bought this boat from original owner (a close neighbor I know and trust) and I know for a fact that it has original engine/head, etc...nothing's been changed out. Confirmed this by comparing all decals and serial #'s across the engine, lower unit, etc. Here's my #'s:<br /><br />Serial #: 0D719950<br /># stamped next to distributor: M10022RJ<br />Casting # on block: 14097080 267 91<br />Wish I could find a casting # on the head, but I cannot.<br /><br />So...if I understand Trog's note above regarding the "RJ", I have a 3.0L block with a 2.5 L head, right?<br /><br />What I don't quite understand is the 115 vs 135 #'s game. Assuming Trogs facts are correct, would it not make perfect sense that getting a newer model LX 3.0 head, and replacing my 2.5 head, would help me to gain another 20 horse?<br /><br />In cars, the head is everything...for the same reason a few years back Ford sold a 3.0L base Taurus GL putting out 140HP, and as an option you can buy a 3.0L 200HP Taurus LX. The only difference was the heads, intake, and exhaust...they flowed air better...with the exact same block. No superchargers or anything silly needed.<br /><br />Is this not the same concept here? Seems like an easy HP gain would be to put the more current heads on. Or would it not work? And why?<br /><br />Thanks again for some great insight. I'd LOVE to hear from someone close with Mercruiser to tell me the real juice here on all this. And actual Dyno #'s for various combinations would be outstanding data if they exist somewhere.<br /><br />Great forum, I'm gonna like it here....
 

MrBill

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Re: How to convert a 3.0L to a 3.0LX?

Use this link to look up Mercruiser engines, including serial numbers and part numbers to validate specific parts, years, etc.<br /><br /> http://www.mercruiserparts.com/selectModels2.asp?type_id=4 <br /><br />Bondo is right-on, rule of thumb to increase speed is each 15HP = 2 additional miles per hour.<br /><br />So when the spending begins...if $1000 = 15 additional HP, then $1000 = 2 MPH.<br /><br />Boating Magazine recently (September / October) had an article about getting increased speed by tweaking hulls, supposedly money better spent. The example they used got 3-4 miles per hour gain for $600 investment. I'm going by memory here, but small performance gains, increases of 2 to 6 miles per hour, can be more cost effectively achieved with minor modifications to the hull. Changes to the hulls planing surface shape can make big differences, particularly on older boats whose hull planing surface has convexed as a result of age and stress. If ther's interest I'll dig out the exact article and other info.
 

craze1cars

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Re: How to convert a 3.0L to a 3.0LX?

Great site Mr. Bill...thanks for the info. That helped explained things very well. As I suspected, Mercruiser specifies 2 different head part #'s for the 1990 to 1994 3.0. One part # for the 3.0L, and one for the 3.0LX. So the LX has to be the one that flows better as it's rated 20hp more.<br /><br />While I certainly understand and appreciate the $ outlay that may be needed for a many people to do these mods, that is not an issue for me as I have access to a boat salvage yard with parts for little to nothing. I also recognize that a 4.3, 5.0, or 5.7 boat would crank up HP quick, too. But this boat is going to be more of an experiment than a daily driver. I also have my own machine shop and I rebuild engines all the time. I've built 350 Chevys that crank out nearly 600 horse, and Honda Civic 4 cylinders that produce over 400hp,...so I know there's gotta be a lot of potential with these massive 3.0 bores. The downside is there does not appear to be any source of engine aftermarket parts as I could find for the Chevy or Hondas, so I understand it will take some creativity and fabrication. So I guess my first simple question is this...if I can score a good used LX head for free, recondition it and bolt it on myself for nothing more than the cost of some gaskets and my time, will I indeed gain 20hp? Or do other mods need to be done as well? Anyone ever tried to do some porting/polishing of an existing 3.0 head? Different rocker arm ratios? Cam angles? I could easily do this work too for almost free, but would be curious of starting points and dimensions if anyone's tried it. Often building higher HP in small displacement motors results in lower torque on the bottom end...I'm sure that's critical in boats also as they have no choice but to plane at lower RPMs as there's no clutch or high RPM stall converter to help keep it in it's powerband.<br /><br />Anyone out there worked with issues like this? Surely there's a few other gearheads like myself out there who have done some non-conventional things with these motors internally to get some more juice out of them. What's worked, what hasn't, and what's caused you to blow 'em up?<br /><br />I'm looking forward to playing with this thing for a while. Hope this explains what I'm seeking a little better.<br /><br />See ya!
 

MGallik

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Re: How to convert a 3.0L to a 3.0LX?

For as much as you'd like to get into the 3.0 why not get a 4.3? If the engine was an option on that boat, it will fit. There's parts all over Ebay for them.
 

TilliamWe

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Re: How to convert a 3.0L to a 3.0LX?

Craze you stated<br /><br />
Ford sold a 3.0L base Taurus GL putting out 140HP, and as an option you can buy a 3.0L 200HP Taurus LX. The only difference was the heads, intake, and exhaust...they flowed air better...with the exact same block. No superchargers or anything silly needed.<br />
Well, they still use two 3.0 v6 engines. The "Vulcan" v-6 is the lower powered of the two. The other "Duratec" is the 200hp one. Not being a Ford guy, I can not say for certain that the blocks are the same, but as the husband of the owner of a 1997 Taurus with the Duratec, I can say this:<br />It is a Dual Overhead Cam engine. So while "only" the heads are different, they are WAY different! So it's not like they ported & polished the heads of the Vulcan and got 40hp. They changed the valve train completely. And made a much more expensive engine.<br /><br />I am not attacking you. I am just pointing out that you are gonna struggle to get much more HP out of that 3.0.
 

craze1cars

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Re: How to convert a 3.0L to a 3.0LX?

No prob...with the Taurus, I had just pulled a rough example out of the air. I'm not a Ford guy by any means and you may be absolutely right. But it's very true that people have been putting 427 heads on 396 Chevy blocks, and 455 heads on 400 Pontiac blocks, etc. And you can take a stock Chevy 350 head, replace it with aftermarket Edelbrock Aluminum heads, and gain around 100 horse real easy with no block mods. And porting/polishing heads to gain significant power is as old as racing is. Engines are nothing but big air pumps, and heads control the air flow, so they're everything when it comes to making power, and that's where I'm real curious about these 3.0's and the various heads that have been sold with them over the years. Some have gotta flow better than others, because the main 3.0 block appears to be pretty much identical all along and horsepower ratings have varied from 115 to 140.<br /><br />I happen to have a 3.0 115. So I figure it can't be that hard to make it into a 135 or 140 with a different head. I'm trying ot figure out which one is best, and IF it would work at all. But maybe I'm totally wrong...that's why I'm asking the ?'s. Seems I haven't found someone with a definitive answer yet.<br /><br />Thanks for your input.
 

TilliamWe

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Re: How to convert a 3.0L to a 3.0LX?

You are not totally wrong, far from it. You are probably very mostly right. But unfortunately, you are applying tried & true hotrod techniques to a motor noone seems to care about! My guess is that nobody knows which of the 6 heads is the best. And if they are anything like 350 heads, the ones that flow the best will have drawbacks like higher possibility of cracking.<br />Also, isn't the intake and exhaust on the same side of the head? That makes it difficult to upgrade either mainfold. But breathing is key to power, as you know.<br />You also hit a big nail on the head with the need for torque in a boat. A high revving screamer is not gonna be the best motor in a boat. That's why Mercruiser came up with that 470/485. It a 223 cu in 4 cyl! Good HP, but also had great torque, do to the cubes. But shook like a paint mixer!
 

Bondo

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Re: How to convert a 3.0L to a 3.0LX?

To the Best of My reckalection, the head I sold to a local machineshop was off of a '74, 181cid, 140hp.........<br />It's ports were 1/2" taller than the cracked head on the 3.0l he was rebuilding..... Andy says, "As long as the manifold covers the ports, It'll Work".......... It Did.....<br /><br />Another Thought......<br />Have the newest 3.0l heads been updated to the Vortec ports,+ Chambers ??????<br />There's No Better heads for the SBC to get the Best Torque.....<br /><br />A year or so ago, there was a Turbo set-up for a 3.0l on ebay.......<br />There's a thread on it in the achrives...... Check it out....<br /><br />You Limiting Factor in all this is about 5000rpms, is All the drive wants to use..........<br /><br />Have Fun.........<br /><br />I Found My Thrills in a 4.3LX up-grade.......... :D
 

craze1cars

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Re: How to convert a 3.0L to a 3.0LX?

Originally posted by TilliamWe:<br /> But unfortunately, you are applying tried & true hotrod techniques to a motor noone seems to care about! My guess is that nobody knows which of the 6 heads is the best.
I'm sure that you're absolutely correct...but I've always been a wierdo who likes to mess with the unconventional. I know I'm the only grey haired guy running a Civic at the import drags against a bunch of teenagers! I'm an old hotrod guy at heart who luvs to mess with big V8's, but somehow I got intrigued by juicing up 4 cylinders, too. And those monster bores in these 3.0's have me curious about what they can do. I'm sure the big bores are all about torque, as you said, so I need to keep torque preservation in mind if I try some mods. Would love to see HP/Torque curves for these various engines combos if anyone knows of a source.<br /><br />After futher studying part #'s from the website provided earlier in this post, I've determined that primarily the 3.0L and 3.0LX had different heads and different carbs. The rest of the parts all look exactly the same, blocks & cams absolutely identical, exhaust looked about the same, too. I'll probably screw with this thing yet.<br /><br />I know all about the Vortec heads, too. They're the way to go if available. An interesting thought, but I doubt they've done that for the 3.0 or people'd be talkin 'bout it.<br /><br />And the 5,000rpm limit is an interesting thought I need to remember, too. My 400+HP Civic 4 banger doesn't make ANY torque, and needed a 6 speed tranny to keep it spinning somewhere between 7,000 and 10,000 RPMS or it won't go ANYWHERE. Guess I don't really need to make more HP, I need to make more torque, huh?<br /><br />Thanks for all the thoughts. Keep 'em comin....
 

trog100

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Re: How to convert a 3.0L to a 3.0LX?

i doubt the quoted figures of 115 horse for the 3 litre block with a 2.5 litre head..<br /><br />assuming that it is a standard 2.5 litre head exactly the same as what was fitted to the original 2.5 litre engine quoted at 115 horse.. and i have found nothing to suggest it isnt...<br /><br />the merc manuals only mention two differences between the two engines.. there is the different spakplug reach and only one other difference is mentioned.. the 2.5 head has oil seals on both inlet and exhaust valves the 3.0 has them only on the inlet vales.. lets take this one as a simple cost saving exercise for obvious reason they dont think they are needed on the exhaust valves and have saved a few pence...<br /><br />all valve dimentions are the same on both heads.. the porting is no doubt slightly different one would assume smaller on the 2.5 head but i dont know for sure..<br /><br />the carb is also the same..<br /><br />but there is no real need for say a 2.5 litre engine thats enlarged by 20% to a 3.0 litre to need a different head except for compression ratio problems thow this could be accomodated by the fitting of dished pistons..<br /><br />my logic goes like this.. take a 2.5 engine rated at 115 horse.. bore or stroke it to become a 3.0 litre engine.. leave everything else the same.. now the increase in capacity is 20%.. 20% of 115 horses is 23 horses.. so our 115 horse 2.5 becomes a 115 plus 23 = a 3.0 138 horse engine. <br /><br />now lets not pretend we live in a perfect world and bung some losses in there.. lets knock the theoretical 23 horse power increase down by a factor of 25%.. lets imagine a 15% power increase of 17.25 horses.. errrr.. that still leaves us with a 132.25 horse 3.0l engine... he he he<br /><br />come on dudes wise up.. no way on this planet can sticking a 2.5 head on a 3.0 block otherwise identical to a 2.5 litre block except for its capacity bring it down to the same power output as the 2.5 block with its original head and 500cc less capacity..<br /><br />this 115 horse figure on the 89 to 94 3.0L really has to be pure b-llsh-t and nothing more than a marketing ploy.. as i said earlier they wanted or had to get rid of the 115 horse 2.5 engine block to avoid cutting the number of engines on offer they invented a unicorn and called it a 115 horse 3.0L.. he he he<br /><br />course my other theory about having a whole bunch of 2.5 heads to use up could also be part of the story..<br /><br />this 89 to 94 hybrid 3.0L with a power rating well below what commonsense says it should be is a bit of a mystery and information on it is hard to find.. if anyone has a better explanation than i have come up with as to the "why" of it.. i would be glad to hear it.. personally i think its something merc would sooner not talk about.. he he<br /><br />before someone comes up and says.. well they could have altered something else.. well yes they could have but i really cant find out what and believe me i have certainly tried.. so if anybody knows exactly what else it was they altered to cause this otherwise unexplained power loss please let me know..<br /><br />craze1cars.. your RJ is a 92 to 94 hybrid with the 3.0 block and 2.5 head.. rated 115 horse.. if u believe it.. he he he.. <br /><br />trog100<br /><br />ps.. craze1cars.. the curent 3.0L is rated roughly 130 horse.. all of em from the year dot were except those that ran alongside the 3.0LX tween 89 and 94.. that engine is churning out the same power as it was nearly forty years ago.. no attempt has been made to make it put out more power.. the mystery is why they tried to make it (or claim it did) put out less power for that short four year period.. dyno the bloody thing and find out for sure before u waste time and money trying to turn it bck into what it should have been in the first place..
 

muc

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Re: How to convert a 3.0L to a 3.0LX?

I think they switched from rating HP at the crankshaft to rating HP at the propshaft sometime during these years.
 

trog100

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Re: How to convert a 3.0L to a 3.0LX?

they did muc but that goes back further (early eighties i think) to when they stopped calling the 2.5 engine a 120 and the 3.0 engine a 140.. its not part of this story.. they could have started calling the 120 a 115 and the 140 a 130 but it wouldnt have looked good.. folks expect power output to go up not down.. which probably explains why they went to capacity instead of horsepower in the name.. the 120 became a 2.5L rated at 115 horse and the 140 became a 3.0L rated at 130 horse..<br /><br />trog100
 
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